I have started to offer DS water with his meals (as I now notice food going in, or rather coming out the other end! We are BLW.) but how do I know he is drinking the right amount? He's not constipated or dehydrated, but I'm worried he could fill up on the water and not want milk. He isn't losing weight AFAIK and does have the little baby podge around wrists etc but he is quite small/skinny (as are me and DH) and the HV were worried 2 months ago when I last had him weighed that he was dropping centiles.
I am offering water in an open cup as we didn't get very far with a spout cup. I control the cup so he doesn't tip it everywhere and offer it to him when he reaches for it. (I keep it out of his reach but in his sightline during meals) He has his hands on the cup so he could push it away if he didn't want it but he doesn't and so I'm worrying (probably unnecessarily!) that the novelty of drinking from a cup will cause him to take more than he needs.